Field of the Disclosure
The present subject matter relates to labels that exhibit sensor properties that change when exposed to a stimulus in order to manifest environmental conditions that are sensed by the label, thereby indicating a change in a material such as an article of commerce with which the label is associated.
Description of Related Art
Labels having the ability to be responsive to environmental changes to which the labels are exposed are known. Some such labels are battery powered electronic devices with electric switching and that are relatively expensive and not intended to be disposable, at times designed for multiple uses. Others provide a time indicator by selecting a liquid indicator with a given viscosity that determined the rate of migration of the liquid. Other sensor-type labels include Avery® TTSensor™ labels that have the ability to display an integrated result and/or are sensor active labels. Some of the prior labels are of a two-piece design, having an indicator label and an activator label, and monitoring begins when the activator label is applied to the article of commerce or other material, typically over the indictor label. Visual indicators are typically part of these types of prior systems, such a color changes in response to predetermined exposure conditions such as temperature. Variations include anti-microbial air release active labels, useful for monitoring the integrity of cold-chain perishable materials, such as food; fungicidal packaging to address susceptibility to degradation from moisture exposure; and air or steam release systems incorporating one-way valves.